The preparation of lipid-depleted bacteriorhodopsin

Bacteriorhodopsin, the protein of the purple membrane of Halobacterium halobium, was freed to the extent of 90-95% from the natural membrane lipids without loss of function. The residual lipid corresponded to less than 1 mol/mol of bacteriorhodopsin. Delipidation was achieved by treatment of the purple membrane with a mixture of the detergent dimethyldodecylamine oxide and sodium chloride. The detergent was removed by dialysis or by sucrose density gradient centrifugation. Analysis of the lipids removed and those still bound to bacteriorhodopsin was facilitated by the use of purple membrane preparations labelled with 35S, 32P, or 14C. The composition of the residual lipids associated with bacteriorhodopsin was similar to that of the total lipid in the purple membrane.